Daily rhythms of physiology and behavior in most life forms on Earth are synchronized by natural cycles (mainly light:dark cycles), and are subsequently free-run under constant conditions such as constant darkness. Thus these rhythms are driven by the internal circadian pacemakers that use the physically fluctuating stimuli to measure the passage of time. Disruptions of biological clock cause severe health problems in our society, including jet-lag, insomnia, and shiftwork-related illnesses. The molecular central clock-ticking mechanisms in mammals and fruit flies (Drosophila melanogaster) share a number of common features, suggesting that the central time-keeping apparatus has been conserved throughout long evolutionary path. However, the mechanisms of how the central clocks communicate with the downstream targets that are likely responsible for the overt physiology and behavioral rhythms more directly, are largely unknown. Recent studies led by us revealed that a neuropeptide, pigment-dispersing factor (PDF) is an important circadian messenger derived from the pace-maker neurons, called Lateral Neurons in Drosophila. Considering the complexity of the pace-making system, there should be more than one messenger molecule. Circumstantial evidence suggests that a neuropeptide, adipokinetic hormone (AKH), could be involved in the circadian output pathways in insects. I would like to examine the role of AKH gene in the regulation of circadian rhythms in Drosophila using biochemical and molecular neurogenetic tools. I propose to: 1. Test the hypothesis that AKH gene expression is regulated by central clock-ticking system. Do AKH gene products in wild type cycle in a circadian manner? If so, do clock mutations affect this cycling? Where is the AKH gene expressed? Do clock transcription factors regulate AKH gene expression? 2. Test the hypothesis that the roles of AKH-expressing neurons involve the circadian behavioral rhythms. Does the targeted-ablation of the AKH cells cause abnormal circadian behaviors? Do the over- and misexpression of AKH genes disrupt normal circadian rhythms?